The relationship of umbilical cord pH with the neonatal neurological condition was investigated in a group of 805 appropriate-for-dates (AFD) infants, delivered vaginally at term, and in a subgroup of 205 infants born after uncomplicated pregnancy and delivery ('low-risk' group). The results of the neonatal neurological examination were expressed in a neonatal neurological optimality score (NNOS) and in a neurological classification (normal, suspect and abnormal). In both study groups a significant relation between umbilical arterial pH (pHua) and the difference between maternal venous pH and pHua (delta pHm-ua) on the one hand and neurologically suspect infants and NNOS on the other hand, was found. The percentages of explained variance in NNOS, however, were very low (for delta pH, 1 and 4% in the total and low-risk group respectively). Neurological abnormality was not related to acidaemia at birth. Because of the specific relation between maternal and umbilical pH, delta pH is a less reliable indicator of fetal condition in cases of maternal alkalosis or acidosis. The use of a delta pH corrected with the help of a maternal-fetal pH nomogram, however, only slightly improved the relation with neurological morbidity. It is concluded, that in AFD term infants acidaemia at birth is only slightly related to neonatal neurological morbidity.